Topographical distribution of prostaglandin E receptors in human myometrium

The binding of radiolabelled prostaglandin (PG) F2 alpha and PGE2 by human myometrium was measured in vitro and the distribution and characteristics of the binding sites in non-pregnant and pregnant uteri were studied. PGF2 alpha binding sites were of low affinity (Kd 30 nM) and could be occupied by PG of the E series with higher affinity than PGF2 alpha itself. PGE binding sites were of high affinity (Kd 1.5 nM) and highly specific for PG of the E series, suggesting that they represent true PGE receptors. The concentration of PGE receptors was higher in non-pregnant than in pregnant uteri at term. In non-pregnant uteri the concentration of PGE receptors was highest in the fundus and decreased towards the cervix; in term pregnant uteri the concentration was constant in all areas. In both non-pregnant and pregnant uteri there was a significantly lower PGE binding affinity in cervix than in myometrium from the fundus-corpus area. The concentrations and affinity of PGE receptors were similar during the proliferative and secretory phases of the menstrual cycle and were not influenced by age of the patient. PGE receptors were not influenced by the presence or absence of primary dysmenorrhoea but appeared to be increased in unexplained menorrhagia.     

Alpha-adrenergic receptors in human myometrium during pregnancy

The distribution and mechanisms of alpha-adrenergic receptors have been studied in myometrial preparations from women delivered by cesarean section at term. With the use of the radioligand tritiated dihydroergocryptine, the number of alpha-adrenergic receptors was 210 fmol/mg of protein in the uterine fundus and 195 fmol/mg of protein in the lower uterine segment. Competition experiments showed that 60% of the alpha-adrenergic receptors had properties as alpha 1-adrenergic receptors and 40% as alpha 2-adrenergic receptors. In vitro tension studies verified the existence of physiologically active alpha 1- and alpha 2-adrenergic receptors in the myometrial preparations. alpha 2-Adrenergic receptor stimulation resulted in lowered levels of intracellular cyclic adenosine monophosphate. The intracellular cyclic adenosine monophosphate was further reduced by additional alpha 1-adrenergic receptor stimulation, probably secondary to an activation of calcium-calmodulin-dependent phosphodiesterase.     

Evidence for triiodothyronine receptors in human endometrium and myometrium

Thyroid gland dysfunction in humans may cause various female reproductive tract disorders. Thyroid hormone action is thought to be mediated by high-affinity low-capacity receptor proteins located in the nucleus. The studies detailed in this report were undertaken to determine if uterine nuclei contain specific high-affinity receptors for thyroid hormone. Nuclei from human endometrium and myometrium were prepared by homogenization and centrifugation following routine surgical procedures. With the use of isolated nuclei, binding experiments with 125I-triiodothyronine (T3) revealed a dissociation constant of approximately 1 X 10(-9) M in both endometrium and myometrium with a maximum number of binding sites equivalent to 0.06 and 0.21 pmol/mg of DNA, respectively. The solubilized binding sites were destroyed largely by trypsin treatment. Competition experiments revealed the following relative binding affinities for these nuclear binding sites: L-T3 greater than D-T3 greater than L-thyronine greater than reverse T3. These results indicate the presence in the human uterus of specific high-affinity binding sites with characteristics expected of a T3 receptor and thus raise the possibility that thyroid hormone may exert effects on the uterus through these receptors.     

Increased uterine prostaglandin E receptors in menorrhagic women

PGE receptor concentrations were measured in myometrial samples collected from 10 women at hysterectomy. Five women had normal measured menstrual blood loss (35-44 ml) and the remainder had unexplained menorrhagia occurring in the absence of any uterine, pelvic or general pathology, with losses ranging from 85 to 925 ml. Median PGE receptor concentrations were significantly higher in the women with menorrhagia (1077 fmol/mg protein) than in the women with normal menstrual blood loss (625 fmol/mg protein) and correlated with menstrual blood loss (P less than 0.02). These findings suggest that unexplained menorrhagia may simply be a constitutional variant in some women and that specific and potent PGE uterine receptor antagonists would furnish effective non-surgical treatment for unexplained menorrhagia.     

Increased uterine prostaglandin E receptors in menorrhagic women

Summary. PGE receptor concentrations were measured in myometrial samples collected from 10 women at hysterectomy. Five women had normal measured menstrual blood loss (35–44 ml) and the remainder had unexplained menorrhagia occurring in the absence of any uterine, pelvic or general pathology, with losses ranging from 85 to 925 ml. Median PGE receptor concentrations were significantly higher in the women with menorrhagia (1077 fmol/mg protein) than in the women with normal menstrual blood loss (625 fmol/mg protein) and correlated with menstrual blood loss ( P <0·02). These findings suggest that unexplained menorrhagia may simply be a constitutional variant in some women and that specific and potent PGE uterine receptor antagonists would furnish effective non-surgical treatment for unexplained menorrhagia.     

Prostaglandin E and F2 alpha receptors in human myometrium during the menstrual cycle and in pregnancy and labor

The binding of prostaglandins E1 and F2 alpha has been studied in the human myometrium and cervix during the menstrual cycle and in the myometrium of pregnant patients at term before and during labor. Tritium-labeled prostaglandin E1 and F2 alpha binding was saturable and reversible. Scatchard analysis of tritium-labeled prostaglandin E1 binding was linear, which suggests a single class of high-affinity binding sites with an estimated apparent equilibrium dissociation constant of 2.5 to 5.4 nmol/L and inhibitor affinities of 0.9, 273, 273, and 217 nmol/L for prostaglandins E2, A1, B1, and F2 alpha, respectively. Scatchard analysis of tritium-labeled prostaglandin F2 alpha, binding was also linear, but the affinity of these binding sites was much lower, with an average dissociation constant of 50 nmol/L and inhibitor affinities of 1.6, 2.2, and 11.2 nmol/L for prostaglandins E1, E2, and A1, respectively. In nonpregnant patients, the concentrations and affinities of tritium-labeled prostaglandin E1 binding sites were similar in the myometrium during the proliferative and secretory phases of the menstrual cycle, but the concentration of these sites was much lower in the cervix. The concentration of the tritium-labeled prostaglandin E1 binding sites was significantly lower in the myometrium of pregnant patients at term than in the myometrium of nonpregnant patients. The concentrations and affinities of tritium-labeled prostaglandin E1 binding sites were not significantly different in the upper and lower myometrium of pregnant patients at term or in the myometrium of such patients before and during labor. The concentrations of the tritium-labeled prostaglandin F2 alpha binding sites during the menstrual cycle and in pregnancy at term were similar to those of tritium-labeled prostaglandin E1 binding sites. In addition to confirming the presence of specific prostaglandin E and F2 alpha binding sites in the myometrium, these data also suggest: that specific prostaglandin E binding sites are present in the cervix and that the concentrations and affinities of prostaglandin E binding sites do not change during the menstrual cycle and are similar before and during labor in pregnant patients at term.     

Surfactant stimulates prostaglandin E production in human amnion

Discs of human amnion prepared from nine women delivered by elective caesarean section at term were incubated with and without purified human amniotic fluid surfactant (9 micrograms lipid P/ml), and the output of prostaglandin E (PGE) was estimated by radioimmunoassay. Surfactant stimulated the release of PGE from 3.8 (SD 2.9) to 5.4 (SD 2.5) pmol/mg dry weight/3 h (P less than 0.01). Arachidonic acid accounted for 2% of the fatty acids of surfactant lecithin. These results show that surfactant has a stimulatory effect on amniotic PGE production and that it is an important source of arachidonic acid in amniotic fluid.     

Beta-adrenergic receptors in human myometrium during pregnancy: changes in the number of receptors after beta-mimetic treatment

The concentration of available beta-adrenoceptors has been studied in the myometrium of women treated with terbutaline for premature uterine contractions and in an untreated control group. Myometrial strips were taken at cesarean section from the lower uterine segment and the uterine fundus. The concentration of beta-adrenoceptors was determined with a radioligand binding assay. In untreated women we found no difference in the concentration of beta-adrenoceptors in the uterine fundus compared to that in the lower uterine segment. The cyclic adenosine monophosphate production after beta-adrenoceptor agonist stimulation in vitro was equal in both locations. In the terbutaline-treated women, the binding site concentrations in both the fundus and lower uterine segment were lower compared to those in the control group. The decrease was most pronounced in the fundus where receptor concentration was only half that found in the control group. The results suggest that treatment with beta-mimetics causes a desensitization in the beta-adrenoceptor system of human myometrium during pregnancy. This desensitization may partly explain the limited duration of the relaxant effect of beta-mimetics often seen in the treatment of preterm labor.     

Surfactant stimulates prostaglandin E production in human amnion

Summary. Discs of human amnion prepared from nine women delivered by elective caesarean section at term were incubated with and without purified human amniotic fluid surfactant (9 μg lipid P/ml), and the output of prostaglandin E (PGE) was estimated by radioimmunoassay. Surfactant stimulated the release of PGE from 3·8 (SD 2·9) to 5·4 (SD 2·5) pmol/mg dry weight/3 h (P<0·01). Arachidonic acid accounted for 2% of the fatty acids of surfactant lecithin. These results show that surfactant has a stimulatory effect on amniotic PGE production and that it is an important source of arachidonic acid in amniotic fluid.     

Increased decidual prostaglandin E concentration in human abortion

Prostaglandin E (PGE) concentration was measured in decidual tissue after spontaneous and missed abortion and compared with that obtained from induced abortion. Tissues were obtained by curettage from groups of 10 patients each and PGE was estimated by radioimmunoassay. After spontaneous and missed abortions decidual tissue contained significantly higher mean concentrations of PGE, (486.3 and 66.7 ng/g wet tissue respectively) than after induced abortion (18.6 ng PGE/g wet tissue). It is suggested that an increased rate of PGE biosynthesis or reduced breakdown, or both, may play a role in the mechanism of human abortion.     

Increased decidual prostaglandin E concentration in human abortion

Summary. Prostaglandin E (PGE) concentration was measured in decidual tissue after spontaneous and missed abortion and compared with that obtained from induced abortion. Tissues were obtained by curettage from groups of 10 patients each and PGE was estimated by radioimmunoassay. After spontaneous and missed abortions decidual tissue contained significantly higher mean concentrations of PGE, (486.3 and 66.7 ng/g wet tissue respectively) than after induced abortion (18.6 ng PGE/g wet tissue). It is suggested that an increased rate of PGE biosynthesis or reduced breakdown, or both, may play a role in the mechanism of human abortion.     

Activin betaA-subunit and activin receptors in human myometrium at term and during labour

Objective To measure activin A content and to localise and semi-quantitate activin receptors in human myometrium at term and during labour.
Design Myometrium was collected from non-pregnant women (   n = 6  ), pregnant women at term not in labour (   n = 6  ) and at term in labour (   n = 6  ).
Setting Monash Medical Centre, Melbourne, Australia.
Main outcome measures Tissue lysates of myometrium were analysed for activin A content using an enzyme-linked immunosorbent assay and activin receptor proteins IA, IIA and IIB using Western hybridisation. Activin β_A-subunit and activin receptors were localised in myometrium by immunohistochemistry.
Results Activin A was detected by ELISA in non-pregnant, pregnant and labouring myometrium. Levels were significantly higher in labouring myometrium. The three activin receptors IA, IIA and IIB were detected in all myometrial samples by Western hybridisation. Receptor IA was expressed in significantly higher levels in pregnant myometrium. Receptor IIA was very weakly expressed throughout. The expression of receptor IIB was similar in all three groups. Activin β_A-subunit and all three receptors were localised to the endothelial cells of myometrial blood vessels. Neither activin β_A-subunit nor any of the three activin receptors were immunolocalised to myometrial smooth muscle cells in the three groups. This result was confirmed by Western blotting for expression of activin receptors in isolated myometrial smooth muscle and microvascular endothelial cells.
Conclusion The myometrium is not a target for activin A during late pregnancy or labour. However, activin A may have a role in the regulation of microvascular endothelial cell function in the myometrium.     

Localization and kinetic properties of prostaglandin E1 receptor on the plasma membrane of rabbit myometrium in late pregnancy

The distribution of prostaglandin E1 (PGE1) receptor in various subcellular fractions of pregnant rabbit myometrium was closely related with the distribution of [Na + K]-ATPase, 5'-nucleotidase, and Ca2+-ATPase activities, marker enzymes for plasma membrane, but not with that of NADPH-cytochrome c reductase activity, which is a marker enzyme for endoplasmic reticulum. The specificity of PGE1 receptor was significantly different from those of PGE2 and PGF2 alpha. The PGE1 receptor concentration in the plasma membrane fraction increased significantly from 89.0 to 111.1 fmol/mg protein between the 28th and 30th days of pregnancy. Scatchard analysis of PGE1 receptor revealed a nonlineal plot which indicated the existence of negative cooperativity in a kinetic study.